One of these things is not like the others
Please go to the Question #5 post if you haven't had a chance work on this one yet, since the text below contains the solution.
Yesterday, I added a new element to the blog. I had been a little hesitant to do so, because I don't have direct control over this particular element. And, due to the nature of this new element, I had a suspicion that it could act as a spoiler for some of the puzzles. Sure enough, that very thing happened here.
Yes, I am being deliberately vague. Just to be safe, I won't even mention why I'm being vague. Suffice it to say that, from time to time, some of the elements on the page might give you a clue about the answer to the puzzle.
The answer this time, by the way, has to do with knots. You can tie a figure 8 knot, a fisherman's knot, and an overhand knot, but you can't tie a 5.11a knot because there's no such thing. Rather, 5.11a is a difficulty rating for rock climbing, in the Yosemite Decimal System.